I switched from Mac to PC last November.
There were those things about Apple with the .mac acounts and the full paying for Mac OS X 10.2 that really pissed me off (Altough I got 10.2 for free cause I am in ADC).
But the worsed thing is the pricing for Macs: I just couldn't justify to myself to buy a Mac for almost twice the price for getting a decent PC just to get the better OS.
The gap between Mac OS and Windows isn't quite as much as it used to be since XP, in my opinion.
So I am using a PC for almost 5 months as my main working machine (Still got my old Mac, but didn't used it for quite a while).
There were some times when I hated this PC and regretted the switch. But using OS X, there were also several times I cursed this system (that's why I even thought about switching).
Now, looking back, I am quite happy with my PC. It runs really well, never crashes when I am working on it. Windows XP is not that bad, there are quite a few things I really love about it.
But I keep watching the Mac side, maybe the end of the year Apple has some hardware that makes me switch again, we will see...